The Hype Over Circadian Fasting and Why It Works

Although intermittent fasting may seem like the latest fad diet, plenty of research has found this way of eating to have many health benefits and improve sleep quality.  And, when you time your fast with the moon and eating with the sun those benefits are said to increase.


Simply put, fasting is a period of time where you don’t eat, and we often do it while we sleep  - the exception being those who eat in their sleep or wake in the night for a snack. Usually after dinner many people stop eating until the following day when they break their fast with “break-fast.”  


Some individuals take a more calculated approach to their fasting and strategically plan the time they eat and the time they don’t eat. With intermittent fasting, the fasting period usually lasts between 12 and 24 hours. During this time, no food or caloric beverages are consumed.    


There is a lot of hype surrounding intermittent fasting, and most of it is justified as research has found this type of eating to benefit both the mind and body. For example, a 2019 meta-review concluded that intermittent fasting could reduce cholesterol, inflammation, blood pressure, and the risk of type 2 diabetes. Many doctors and dieticians can agree that intermittent fasting is good for you, but the why is still considered debatable. 


Some believe intermittent fasting provides these benefits because they promote weight loss due to a calorie restriction. By missing breakfast, for example, you eat fewer calories. The other argument is that our metabolism is still in “caveman mode,” and we weren’t meant to eat every few hours. Similarly, some believe that by temporarily not eating, you can supercharge your metabolism. Another fascinating theory is that we are diurnal animals and should only eat during daylight hours for optimal health and bodily functioning. This theory is known as circadian fasting. 


What is Circadian Fasting?


To understand circadian fasting, you need to understand circadian rhythm. Circadian rhythm is the changes your body goes through in a 24 hour period. This includes physical, behavioral, and mental changes that impact all of your body’s functions, like eating and sleeping. 


You can think of circadian rhythm as an internal clock. When you feel the urge to crawl into bed and sleep on your buckwheat pillow, this is your circadian rhythm telling you it’s time for sleep! This internal clock is located in your hypothalamus and involves thousands of cells that control hormones like cortisol and melatonin. When aligned with your circadian rhythm, your cortisol levels will rise in the morning and before lunch, while melatonin remains low. In the evening, however, melatonin will increase, reaching a high, and cortisol levels will drop. 


Day light and eating help keep this internal clock accurate; however, when these external signals are disrupted they can severely disrupt your bodily functions and hormone levels. 

A great example of this is jetlag.  if you have traveled abroad to a completely different time zone, you have likely experienced it. In this new time zone, you are seeing daylight when your body is used to sleeping and may even be eating heavy meals when you usually fast. When this happens, there is a mismatch between your internal clock and external signals. This can cause the dreaded symptoms of jetlag like fatigue, mental fog, digestive issues, and irritability. 


In 2017, one study had ten men eat early meals for five consecutive days, followed by eating meals late in the day for six days. The researchers found that by switching to later meals, a gene that regulated their circadian clock was delayed. 


Why does circadian fasting work?


When you don’t eat at the right time of day, it can adversely impact your health. More specifically, eating late at night, especially a big meal can be harmful. For example, studies have found that shift workers who eat and are awake at night are more at risk for cardiovascular disease and obesity.   


These negative health effects are caused by disrupted insulin and cortisol signals. While cortisol levels are high, so is your metabolism. This is what your body uses food for fuel. As your cortisol levels decline, so does your metabolism, meaning food eaten later in the day is more likely to be stored as fat. 


When you eat, especially carbohydrates, your blood sugar levels rise, and your body responds by releasing insulin. A 2019 study found that when you eat late at night, the disruption in insulin levels negatively affect your circadian rhythm and cause long-term health issues. 


What is the difference between circadian rhythm fasting and intermittent fasting?


This is where it can get a bit confusing. Circadian rhythm fasting is a form of intermittent fasting, but intermittent fasting isn’t necessarily circadian rhythm fasting. The differentiator is the time of day you eat. Circadian fasting is a lot more strict when it comes to timing as you shouldn’t eat at night.  It also encourages you to break your fast before noon. 


How do I practice circadian fasting?


Circadian fasting is also known as the circadian rhythm diet or sun cycle diet and involves planning meals around the sun. Although there are no hard and fast rules, many experts suggest eating in a ratio of 16:8, meaning 16 hours of fasting and an 8-hour eating window. To be considered circadian fasting, the fasting period should occur when it is dark. For example, you have dinner just before nightfall at around 6:30 pm and don’t eat again until 11:30 am when the sun is up, and you are active. 


It’s important to note, just because you are fasting for 16 hours doesn’t mean you can eat everything and anything for those 8 hours. It is important to still eat a nutritious diet. Start with a balanced breakfast and make this the biggest meal of the day. By starting the day with a large meal instead of ending it with one, you give your body plenty of time to digest. After some time, you can eat lunch which should be a bit smaller than breakfast but bigger than dinner. Dinner will be your smallest meal and should consist of lighter foods.   To maximize the effects, you can also supplement your diet with a multivitamin. A multivitamin will provide your body with all the vitamins and minerals your body needs.  


When you are awake, you can drink water or tea. It is essential to stay hydrated, and some believe an increase in water intake can further the benefits of fasting and flush toxins out. If you want to enhance the sleep benefits of circadian fasting, you can sip on a sleep tea that only contains herbal ingredients.


What are the benefits of circadian fasting?


Following the sun cycle diet will help regulate hormones. It will prevent damaging insulin spikes and reduce your risk of disease. Research has found that this way of eating can have several health benefits, including: 


  • Improved digestive function
  • Better nutrient absorption (your multivitamin will be much more effective!)
  • Reduced inflammation
  • Strengthened immune system
  • Increased weight loss
  • Improved the quality of sleep (you’ll fall asleep faster and stay asleep on your buckwheat pillow)
  • Efficient metabolism
  • Reduced signs of aging
  • Lower blood pressure
  • Increased energy
  • Reduced effects of jetlag


Additionally, some studies have found that when your eating patterns align with your circadian rhythm, you can reduce the symptoms of diseases such as rheumatoid arthritis, metabolic disorders, Parkinson’s disease, and multiple sclerosis. 


The relationship between circadian fasting and sleep


Research has found that those who practice circadian fasting can see an increase in sleep quality within one week. Study participants stated they fell asleep faster, stayed asleep during the night, and felt their sleep was more restful. Further, data found that these individuals spent more time in the REM sleep stage, which improved brain function the following day. 


This diet has proven to be so effective that some have dubbed circadian fasting as “the fast sleep hack.” Those who travel often or work shifts can help counteract the disruption caused by light by timing their meals accordingly. 


We haven’t always had the luxury of microwaves and drive-thru restaurants. At one point in time, humans had to hunt for their food and cook over a fire. Although technology may develop at a rapid pace or bodies do not, and many believe we aren’t built to have a cheeseburger and fries at 9 pm. 


If you have been habitually eating late at night, it can be tough to break these habits. Start slow and substitute late night eats with a sleep tea. The warm beverage can help reduce cravings and the urge to snack and help you drift off to sleep on your buckwheat pillow. Also, don’t stress too much about time and counting down the minutes until you can eat again. Instead, focus on the sun – stop eating when the sun goes down and enjoy a delicious breakfast when the sun rises again.
Back to blog